This invention relates to blends of thermoplastic polymers, and more particularly to flame retardant blends having improved high temperature properties.
Improvement of the flame retardant properties of thermoplastic polymers such as polycarbonates has long been a goal of polymer compounders. Compounds containing phosphorus have been used in compositions with thermoplastic polymers to improve their flame resistance properties. Among the phosphorus compounds useful for this purpose are the bis(diaryl phosphate) esters of dihydroxyaromatic compounds, as illustrated by resorcinol bis(diphenyl phosphate), hydroquinone bis(diphenyl phosphate), and bisphenol A bis(diphenyl phosphate). Certain water soluble phosphoramides have also been used in the textile industry as flame retardant finishes for fabrics.
Phosphorus-containing compounds, however, often have undesirable effects on other physical properties of thermoplastic polymers. For example, phosphorus-containing compounds frequently have undesirable effects on the high temperature properties of polycarbonate and polycarbonate-containing blends, especially those blends also containing addition polymers such as acrylonitrile-butadiene-styrene copolymers (hereinafter referred to as "ABS copolymers"). Said undesirable effects may be demonstrated by a pronounced decrease in glass transition temperature (Tg) of one or more polymer phases. In addition, other physical properties of the blends, such as ductility, are sometimes adversely affected and may require improvement.
There are increasing demands from key industries, such as the electronics and computer industries, for polymer compositions possessing both flame retardant properties and higher heat resistance. Such compositions must also retain other key physical properties, such as adequate flow and impact strength, for applications such as computer housings, computer monitor housings, and printer housings. Another increasing demand is for materials that are rated in the Underwriter's Laboratory UL-94 test protocol as V-0, V-1, or V-2. It is therefore apparent that new resin compositions that meet these and other demands continue to be sought.